1. Field of the Invention
The present invention relates to an electronic endoscope system for imaging an internal body portion using two or more types of illumination light and a method for controlling the same.
2. Description Related to the Prior Art
In the medical field, electronic endoscopes are widely used in medical examinations. The electronic endoscope is provided with an insert section to be inserted into a patient's body. Illumination light is applied to an internal body portion of the patient from a distal end of the insert section. An imaging device disposed in the distal end captures an image of the internal body portion being illuminated.
The electronic endoscope is connected to a lighting device. The illumination light from a light source of the lighting device is supplied to the electronic endoscope. Conventionally, a white light source (e.g. a xenon lamp or a metal halide lamp) has been used. Recently, a technique using narrowband light as the illumination light has attracted attention (see Japanese Patent No. 3583731 corresponding to U.S. Patent Application Publication No. 2008/0281154). The narrowband light is applied to the internal body portion and an image of the reflection light is captured. The use of the narrowband light facilitates finding a lesion.
A method for obtaining vascular information (e.g. an oxygen saturation level of hemoglobin in blood) based on image signals of images has been researched (see Japanese Patent Laid-Open Publication No. 06-315477). In this method, the images are captured under the illumination of the respective different types of narrowband light applied alternately. The method utilizes the narrowband light of wavelength sets in the respective wavelength bands of 300 to 400 nm, around 400 nm, 400 to 500 nm, 500 to 600 nm, and 450 to 850 nm.
A semiconductor light source (e.g. a semiconductor laser diode) has been used for a narrowband light source. Frequent turning on and off of the semiconductor light source causes overshoot of its output mainly due to temperature factors. In other words, a light quantity of the illumination light increases instantaneously after the turning on, making the light quantity unstable and uneven. Thereby, accurate vascular information cannot be obtained. The U.S. Patent Application Publication No. 2008/0281154 and Japanese Patent Laid-Open Publication No. 06-315477 do not disclose solution to the problem.